Fixed primer set-back cartridge



Nov. 11, 1969 a. RQBARR 3,477,374

FIXED PRIMER SET-BACK CARTRIDGE Filed April 11, 1968 I 2 Sheets-Sheet 1 Irwin R. Barr INVENTOR ATTORNEY Nov. 11,1969 LRB RR 3,477 1 FIXED PRIMER SET-BACK CARTRIDGE Filed April 11, 1968 2 Sheets-Sheet 2 /rw/' n R. Barr INVENTOR BY fla M ATTORNEY United States Patent 3,477,374 FIXED PRIMER SET-BACK CARTRIDGE Irwin R. Barr, Lutherville, Md., assignor to AAI Corporation, Cockeysville, Md., a corporation of Maryland Filed Apr. 11, 1968, Ser. No. 720,559 Int. Cl. F42b 5/28 US. Cl. 10245 8 Claims ABSTRACT OF THE DISCLOSURE A cartridge is disclosed having a single-unit primer fixedly disposed in the base portion of a propellant containing cartridge casing for use in automatic and semiautomatic firearms which operate on the principle of primer set-back. The primer is open toward the interior of the cartridge casing and has a rearwardly protruding cup-shaped piston portion containing a primer charge that is adapted to be deformed into a circumferential rim anvil upon being struck by the head of a firing pin to ignite the primer charge contained therein and fire the propellant contained in the cartridge casing to create a high propellant gas pressure which in turn causes the piston portion to expand rearwardly and drive the firing pin backward.

This invention relates to cartridges of the primer setback or piston-primer type.

In automatic, or semi-automatic firearms utilizing primer set-back cartridges for operation, a cartridge may be chambered in the barrel, and When the firing pin of the firearm strikes the primer in a forward stroke, a primer charge ignites which, in turn, ignites a propellant to create a high gas pressure that propels a projectile forward from the cartridge casing and through the barrel. In addition, the high gas pressure causes the primer to impart energy to the firing pin and drives it backward in a return stroke which operates the breech mechanism to extract the spent cartridge casing, cock the firearm and chamber another cartridge.

To obtain the most efiective operation of a primer set-back arrangement, it is necessary to use a cartridge which maximizes the amount of energy the primer imparts to the firing pin of the firearm during the return stroke. This can best be done by avoiding energy losses resulting from the friction between the primer and the cartridge casing, e.g. is inherent in a cartridge of the type utilizing a movable primer to drive a firing pin backward in a return stroke, while at the same time preventing the propellant gas from leaking rearward of the primer which would substantially reduce the differential gas pressure exerted on the primer and which is particularly a problem in cartridges utilizing a movable primer which necessitates the use of some type of movable gas seal. Furthermore, it is desirable to prevent the primer from being blown out the base of the cartridge because the resulting sharp reduction of the propellant gas pressure would substantially reduce the velocity of the projectile and hence affect the range and accuracy of the weapon. In addition, it is desirable that the primer be constructed of as few parts as possible to facilitate the manufacture of the cartridge and reduce the production costs.

Accordingly, it is a feature of the present invention to provide a cartridge of the primer set-back type wherein energy losses due to the friction between the primer and the cartridge casing are avoided while efficiently translating propellant gas pressure action into a rearward driving force on the primer; thereby enabling a maximum driving force to be imparted to the firing pin of the firearm during the return stroke.

It is another feature of the present invention to provide a primer which engages the cartridge casing in a manner that prevents the rearward leakage of the high pressure propellant gas to further maximize the amount of force exerted on the piston primer and also prevents the primer from being blown out the base of the cartridge by the propellant gas force.

It is a further feature of the present invention to provide a primer having a simple, compact and unitary construction to facilitate the manufacture of the cartridge and reduce the production costs. 7

In accordance with the present invention a cartridge casing is provided containing a propellant and having a bore formed in the base with a single unit primer fixedly disposed therein which opens toward the interior of the casing and contains a primer mixture adapted to be ignited to fire the propellant contained in the casing. The primer has a rearwardly protruding cub-shaped piston portion that is adapted to be deformed into a circumferential rim anvil to ignite the primer charge! contained therein and subsequently expand rearwardly.

When the head of the firing pin strikes the base of the rearwardly protruding cup-shaped primer at the end of a forward stroke, the piston portion is deformed into a circumferential rim anvil that is crushed to ignite the primer charge, which in turn fires the propellant to create a high gas pressure that propels the projectile from the cartridge while at the same time causes the piston portion to expand rearwardly and drive the firing pin back in a return stroke. Due to the tight gas-sealing fit of the primer in the cartridge which prevents the propellant gas from leaking rearward of the primer and the lack of any loss of energy due to friction between the primer and the cartridge casing, the rearward expansion piston portion of the primer drives the firing pin backward in a return stroke and transfers a maximum amount of energy to operate the breech mechanism, extract the spent cartridge, cock the firearm, and chamber another cartridge.

Still other objects, features and attendant advantages will become apparent to those skilled in the art from a reading of the following detailed description of several physical embodiments constructed in accordance with the present invention, taken in conjunction with the accompanying drawings wherein:

FIG. 1 shows a longitudinal cutaway view of a cartridge according to the invention.

FIG. 2 shows the cartridge of FIG. I inserted in the chamber of a firearm with a bolt engaging the base of the cartridge and having a firing pin in the ready position.

FIG. 3 is a view similar to FIG. 2 showing the firing pin shortly after striking the base of the primer and igniting the propellant to provide the projectile-propelling high gas pressure.

FIG. 4 is a view similar to FIGS. 2 and 3 showing the base of the cartridge casing and the primer is fixedly disby the propellant gas pressure to force the firing pin backward in the return stroke.

FIG. 5 illustrates a second embodiment according to the invention wherein a conical recess is formed in the base of the cartridge casing and the primer is fixedly disposed in the cartridge casing by the friction resulting from the radial expansion caused by the high pressure propellant.

FIG. 6 illustrates a third embodiment according to the invention wherein a conical recess is formed in the base of the cartridge casing and the primer is fixedly disposed in the cartridge casing by screw threads.

FIG. 7 illustrates a fourth embodiment according to the invention wherein a conical recess is formed in the base of the cartridge casing and the primer is fixedly disposed therein by friction and radial deformation into annular grooves formed in the cartridge casing caused by the high pressure propellant.

Referring now in detail to the figures of the drawings, in FIG. 1 is shown a cartridge suitable for use in a firearm which is operated on the primer set-back and energy transfer principle. The cartridge, generally indicated at 11, includes a casing, generally indicated at 13, containing a single-unit piston primer, generally indicated at 15, a projectile 21, and a propellant 31 disposed between the piston primer 15 and the projectile 21. In the forward portion of the cartridge casing 13 is formed a propellant-containing cavity 1306 which is adapted to securely grip an annualr groove 21a of the projectile 21 by means of an annular indentation 13b. In the base of the cartridge casing 13 is formed a cylindrical recess 13c which is connected by means of an annularshoulder 13d to a bore 13e which opens to the rear of the cartridge casing 13. The cylindrical recess is also connected by means of an annular shoulder 13 to a cylindrical port 13g which opens to the propellant-containing cavity 13a in the forward portion of the cartridge casing 13.

Disposed inside the cylindrical recess 130 is a single-unit piston primer 15 having a relatively thick tubular wall 15a with an outer diameter and length that engages the interior diameter and the forward and rearward annular shoulders 13 and 13d in a tight gas-sealing fit to prevent any rearward propellant gas leakage while also fixedly maintaining the longitudinal position of the primer 15 in the base of the cartridge casing. The single-unit cupshaped piston primer 15 is open towards the interior of the cartridge casing and contains a primer mixture 17 which is separated from the propellant 31 by only a thin, easily frangible and preferably combustible moisture seal 19 of suitable material such as a coating of wax or Krylon. While the moisture seal 19 is not absolutely required for functional operation, it is desirable to aid against malfunction due to undesired moisture absorption by the primer mixture which, for example, might occur during assembly of the cartridge.

At the reaward end of the tubular wall is formed a conical recess or annular beveled shoulder 15b that tapers inwardly to a rearwardly protruding cup-shaped piston or base portion 150 relatively thinner and more easily deformable than the tubular walls. Upon being struck by the head of a firing pin, the cup-shaped piston portion 150 is adapted to be deformed and pressed against the wall of the conical recess 15b which serves as an effective circumferential anvil and, in conjunction with the firing pin, provides a tight fitting internal chamber seal to prevent the relatively thin-walled piston portion 150 from being laterally ruptured by the high gas pressure resulting from the ignition of the propellant 31.

In FIGS. 2-4 is illustrated the operation of the cartridge 11 shown in FIG. 1. In FIG. 2, the cartridge 11 is shown inserted in a chamber 410: of a conventional barrel 41 having a bore 43 with a bolt 51a pressed against the base of the cartridge casing 13 and having extractor fingers 51a engaging an extractor groove 13f formed in the rear of the cartridge casing 13. Disposed inside the bolt 51 is a firing 61 having a head 61a for striking the base of the readily deformable rearwardly protruding cup-shaped piston portion 15c of the primer 15 to cause ignition of the primer charge 17 to fire the propellant 31.

In FIG. 3 is shown the head 61a of the firing pin 61 striking the base 150 of the piston portion of the cupshaped primer 15 at the end of a forward stroke. The rearwardly protruding piston portion 15c is crushed and pressed against the wall of the conical recess 15b formed at the rearward end of the tubular wall portion of the primer 15 which effectively serves as a circumferential rim anvil thereby igniting the primer charge. In addition, the head 61a of the firing pin 61 and the wall of the inwardly tapering conical recess co-act to provide a seal which prevents any lateral rupture of the relatively thin-walled piston portion 150 of the cup-shaped primer 15. The ignition of the primer charge 17 fires the propellant 31 which generates a high gas pressure that propels the projectile 21 forward away from the cartridge casing 13. Leakage of the high pressure propellant rearward through the bore in the base of the cartridge 11 is prevented by the tight gas-sealing fit by which the primer 15 is disposed inside the cylindrical recess 130 in the base of the cartridge casing 13.

As the high pressure gas propels the projectile 21 forward through the barrel 41, it also exerts a pressure throughout the interior of the primer 15 and causes the relatively thin and easily deformable piston 15c to expand rearwardly into a semispherical shape as shown in FIG. 4. The rearward motion of the expansion of the cupshaped piston portion drives the firing pin 61 backward in a return stroke to operate the breech mechanism and/ or other components of the firearm.

In FIG. 5 is shown another embodiment of a cartridge 11 suitable for use in a firearm employing the primer setback and energy transfer principle. In this embodiment, generally indicated at 111, a bore 113a is formed in the base of the cartridge casing 113, which is connected by an annular beveled shoulder 113b which serves as a conical recess to a coaxial and larger diameter bore 113:: which opens to the rear of the cartridge casing 113. The smaller diameter bore 11311 is also connected by means of an annular shoulder 113d to a cylindrical port 113e, which opens to a propellant-containing cavity 113] in the forward portion of the cartridge casing 113. Disposed inside the smaller diameter bore 1130: in a tight interference fit and protruding rearwardly into the conical recess 113b and the large diameter bore 1130 is a cup-shaped piston primer generally indicated at 115 which is open at the forward end and engages the forward annular shoulder 113d. Compacted inside the cup-shaped piston primer 115 is a primer charge 117 which is separated from a propellant 131 contained in the forward portion of the cartridge casing 113 by only a thin, easily frangible, preferably combustible moisture seal 119 of suitable material such as wax or Krylon.

Upon being struck by the head of a firing pin at the end of a forward stroke, the rearwardly protruding cupshaped base portion of the primer 115 is adapted to be inwardly deformed and pressed against the annular beveled shoulder 11312 which forms the inwardly tapering conical recess and serves as a circumferential anvil, thereby igniting the primer charge 117 which in turn fires the propellant 131 contained in the cavity in the forward portion of the cartridge casing 113 to create a high pressure gas that propels a projectile forward while at the same time eifecting a rearward expansion and energy transfer motion of the cup-shaped piston portion 115 as hereinbefore described in relation to the cartridge shown in FIG. 1. The primar 115 is retained in the base of the cartridge casing 113 by the friction between the primer 115 and the small diameter bore 113a resulting from radial expansion of the wall of the primer 115 caused by the high pressure propellant.

In FIG. 6 is shown still another embodiment of a cartridge suitable for use in a firearm employing the primer set-back and energy transfer principle. In this embodiment, generally indicated at 211, a bore 213a is formed in the base of a cartridge casing 213, which is connected by an annular beveled shoulder 213b which serves as'a conical recess to a coaxial and larger diameter bore 2130 which opens to the rear of the cartridge casing. The smaller diameter bore 213a is also connected by means of an annular shoulder 213d to a cylindrical port 213e which opens to a propellant-containing cavity in the for-- ward portion of the cartridge casing 213. Screw threads 213 are formed in the small diameter bore 213a which extend longitudinally throughout a portion of the length of the bore from the rearward end thereof. Disposed inside the smaller diameter bore 213a and protruding rearwardly into the larger diameter bore 2130 is a cup-shaped piston primer 215 having screw threads 215a formed on the exterior surface throughout part of its longitudinal length which engage the threads 213 of the small diameter bore 213a and which is open at the forward end and engages the forward annular shoulder 213d. Compacted inside the cup-shaped piston primer 215 is a primer charge 217 which is separated from a propellant 231 contained in the forward portion of the cartridge casing 213 by only a thin, easily frangible, preferably combustible moisture seal 219 of suitable material such as wax or Krylon.

Upon being struck by the head of a firing pin at the end of a forward stroke, the rearwardly protruding cupshaped base portion 215 is inwardly deformed and pressed against the annular beveled shoulder 213b which forms an inwardly tapering conical recess and serves as a circumferential anvil thereby igniting the primer charge 217 which in turn fires the propellant 231 contained in the interior of the cartridge casing 213 to create a high pressure gas that propels a projectile forward from the cartridge 211 while at the same time effecting a rearward expansion and energy transfer motion of the readily deformable cup-shaped piston portion 215 as hereinbefore described in relation to the cartridge shown in FIG. 1. The primer 215 is retained in the small diameter bore 213a by the screw threads 215a and 213 in addition to the friction between the primer 215 and the small diameter bore 213a resulting from the radial expansion of the wall of the primer 215 caused by the high pressure propellant.

In FIG. 7 is shown a further embodiment of a cartridge suitable for use in a firearm employing the primer setback and energy transfer principle, In this embodiment, generally indicated at 311, a bore 311a is formed in the base of a cartridge casing 313, which is connected by an annular beveled shoulder 313b which serves as a conical recess to a coaxial and large diameter bore 3130 which opens to the rear of the cartridge casing. The small diameter bore 313a is also connected by means of an annular shoulder 313d to a cylindrical port 313e which opens to a propellant-containing cavity in the forward portion of the cartridge casing 313. Screw threads or annular grooves 313 are formed in the small diameter bore 313a which extend longitudinally throughout a portion of the length of the bore. Disposed inside the smaller diameter bore 313a and protruding rearwardly into the larger diameter bore 3136' is a cup-shaped piston primer, generally indicated at 315, which is open at the forward end and engages the forward annular shoulder 313d. Compacted inside the cup-shaped piston primer 315 is a primer charge 317 which is separated from a propellant 331 contained in the forward portion of the cartridge case 313 by only a thin, easily frangible, preferably combustible, moisture seal 319, of suitable material such as wax or Krylon.

Upon being struck by the head of a firing pin at the end of a forward stroke, the rearwardly protruding cupshaped base portion 315 is inwardly deformed and pressed against the annular beveled shoulder 313b which forms an inwardly tapering conical recess and serves as a circumferential anvil, thereby igniting the primer charge 317, which in turn fires the propellant 331 contained in the interior of the cartridge casing 313 to create a high gas pressure that propels the projectile forward while at the same time effecting a rearward expansion and energy transfer motion of the deformable cup-shaped piston portion 313 as hereinbefore described in relation to the cartridge shown in FIG. 1. The primer 315 is retained in the base of the cartridge casing 313 by the radial expansion of the primer wall due to the high pressure propellant which deforms the primer wall against the screw threads 313i to form interfitting screw threads in addition to causing friction between the primer 31S and the small diameter bore 313a.

That which is claimed is:

1. In a cartridge of the primer set-back type including a casing having an open forward end with a projectile fastened therein containing a propellant and having a bore formed in the base portion with a piston primer disposed therein and having a piston portion adapted for longitudinal movement along the axis thereof, the improvement comprising:

a cup-shaped piston primer containing a primer mixture and being fixedly disposed in said bore and having a forward end open towards the propellant contained in the cartridge casing and a rearwardly extending base portion adapted to be deformed into a circumferential rim anvil and pressed against the wall of a conical recess upon being struck by the head of a firing pin to ignite the primer mixture contained therein and fire the propellant to create a high gas pressure and effect a rearward expansion of the cupshaped piston base portion to drive the firing pin rearwardly in the opposite direction.

2. In a cartridge of the primer set-back type according to claim 1, comprising:

said conical recess being formed in the base portion of said cartridge casing coaxially with the bore formed therein.

3. In a cartridge of the primer set-back type according to claim 2, further comprising:

a first screw thread being formed partially throughout the longitudinal extent of the bore formed in the base of said casing, and

a second screw thread being formed on the exterior surface of the piston primer and adapted to engage said first screw thread formed in the bore in the base of said casing to enable the piston primer to be fixedly disposed in the bore of the base of said casing.

4. In a cartridge of the primer set-back type according to claim 2, further comprising:

said cup-shaped piston portion having a tubular wall adapted to engage the bore formed in the base of said casing in a light interference fit and adapted to expand radially upon ignition of the primer mixture and propellant to create a sufiicient frictional force between the exterior tubular wall of the primer and the bore in the casing to fixedly maintain the primer in the base of the casing.

5. In a cartridge of the primer set-back type according to claim 1, wherein:

said cup-shaped piston portion has a tubular wall adapted to engage the bore formed in the base of said casing in a light interference fit and adapted to expand radially upon ignition of the primer mixture and propellant to create a sufiicient frictional force between the exterior tubular wall of the primer and the bore in the casing to fixedly maintain the primer in the base of the casing.

6. In a cartridge of the primer set-back type according to claim 1, comprising:

screw threads being formed partially throughout the longitudinal extent of the bore formed in the base of said casing, and

screw threads 'being formed on the exterior surface of the piston primer and adapted to engage the screw threads formed in the bore in the base of said casing to enable the piston primer to be fixedly disposed in the bore of the base of said casing.

7. In a cartridge of the primer set-back type according to claim 1, comprising:

a cylindrical recess formed in the base of said casing coaxially with the bore formed therein, and

said primer having a tubular wall portion relatively thicker than the rearwardly protruding cup-shaped piston portion and adapted to be disposed in a gassealing interference fit in the cylindrical recess formed in the base of said casing.

7 8 8. In a cartridge of the primer set-back type according References Cited to claim 7, further comprising: UNITED STATES PATENTS a conical recess formed in the rearward en d oi the tubu- 624,146 5/1899 Young 1O2 38 lar wall portion of said primer coaxrally w th the 740 790 10/1903 Young et a1. 10245 rearwardly protruding cup-shaped piston portion to 5 2 394 249 2/1946 McGahey 1O2 38 provide a wall against which the cup-shaped piston 2:537:443 1/1951 Cerrena portion may be pressed to ignite the primer mixture 7 contained therein. ROBERT F. STAHL, Primary Examiner 

